New copoly(aryl ether ketone)s have been synthesized by polycondensation of 2,2',3,3',6,6'-hexaphenyl-4,4'-diphenol, 2,2'-p-hydroxyphenyl-iso-propane, and 4,4'-difluorobenzophenone. The technology of C-13-NMR was used to determine contents of the two bisphenols in the copolymers. Chain structure was characterized by illustrating average block length (L-A, L-C) in terms of portion of the triads (AKA, CKC, AKC). The obtained copoly(aryl ether ketone)s have the properties of excellent solubility, high heat-resistance, good tensile strength, and good selectivity for gas permeability.